Percutaneous angioplasty is a therapeutic medical procedure than can increase blood flow through a blood vessel. It can sometimes be used as an alternative to coronary by-pass surgery, for example. An elongated catheter having a deflated balloon at its distal end is guided through a patient's cardiovascular system to the coronary artery of the heart. The balloon is inflated to compress deposits that have accumulated along the inner walls of the coronary artery to widen the artery lumen and increase blood flow.
A known technique for positioning the balloon catheter uses an elongated guidewire that is inserted into the patient and routed through the cardiovascular system as guidewire progress is viewed on an x-ray imaging screen.
Representative prior art patents that disclose flexible, elongated guidewires are U.S. Pat. Nos. 4,545,390 to Leary, 4,538,622 to Samson et al. and 3,906,938 to Fleischhacker. The Leary '390 patent discloses a narrow flexible guidewire having a distal portion that tapers and includes a flexible coiled spring at its distal end. Also representative are U.S. Pat. No. 4,846,186 to Box et al. and U.S. Pat. No. 5,267,574 to Viera et al., both of which are incorporated herein by reference.
One problem with currently available guidewires concerns the visibility of the guidewire. If the guidewire is fully opaque on a viewing screen, it can hinder viewing of post angioplasty angiograms used in studying the results produced by the angioplasty. Guidewires that have only an opaque tip do not adequately depict the arterial path on the viewing monitor.
One prior art guidewire includes an elongated core wire including a flexible reduced diameter distal end and a spring made up of multiple coils of wire wound to form a first, generally uniform diameter spring portion. The spring is constructed of a radiopaque material so that the tip of the guidewire is radiopaque when viewed on a fluoroscope or an x-ray. Most preferably, only a short segment of the guidewire (approximately 3-5 cm) is radiopaque so that the physician's view of the subject just proximal of the guidewire tip is not impeded.
Guidewires have been proposed which, in addition to a fully opaque tip, include an adjacent section of lesser radiopacity. This adjacent section is constructed to achieve a lesser degree of radiopacity by means of alternating radiopaque and non-radiopaque coils, or by means of a plurality of individual radiopaque rings attached to the core of the guidewire.
More particularly, in one prior art guidewire, a plurality of highly radiopaque rings are spaced from each other along a segment of the core wire adjacent to the distal portion of the guidewire having the radiopaque spring. In this way, this adjacent portion of the guidewire is provided with a moderate degree of radiopacity. The rings in this adjacent section can be held in place under a sleeve of non-radiopaque material. The rings aid an attending physician in monitoring the position of the guidewire. A problem with this guidewire is that in manufacturing, it is necessary to provide a step of attaching each of the individual rings to the core. This can be burdensome and costly.
In the prior art there has also been proposed alternating radiopaque and non-radiopaque coils around the segment of the core wire proximal to the distal spring portion of the guidewire. The radiopaque coil can be formed from a highly radiopaque metal, and the non-radiopaque coil can be formed from a flexible non-radiopaque polymer. The distal spring portion of the guidewire is formed solely from a radiopaque material so that the resulting guidewire provides a distal spring having high radiopacity, as well as a proximal section of moderate radiopacity. When constructing such a guidewire, steps must be followed for attaching the alternating radiopaque and non-radiopaque coils to the guidewire core, which can be difficult and detrimental.